1. Field of the Invention
This invention relates to inhibitors of bacterial sialidases. In particular, this invention provides novel inhibitors to bacterial sialidases, methods of making the inhibitors, methods of treatment using the inhibitors and methods of prophylaxis from bacterial infection using the inhibitors.
2. Background of the Invention
Sialidases (acylneuraminyl hydrolases, EC 3.2.1.1 8), also known as neuraminidases, are enzymes which cleave the .alpha.-ketosidic bond between a terminal sialic acid residue and an aglycon moiety. The aglycon is usually the penultimate sugar residue of a glycoconjugate or glycoprotein carbohydrate chain. The first sialidase was purified and characterized from the influenza virus and the bacteria Vibrio cholerae [Gottschalk, A. (1957). Neuraminidase: The Specific Enzyme of Influenza Virus and Vibrio cholerae. Biochirn Biophys Acia., 23, pp. 645-646]. Today, sialidases specific for varying ketosidic linkages have been identified in viruses, bacteria, parasites, and mammals. They play a critical role in viral, bacterial, and protozoa biology by mediating metabolism, adherence, and-infection, and are important regulators of alternate complement pathway activation, red blood cell destruction, cell growth, cell adhesion, and tumor metastasis in mammalian systems.
Therefore, the development of sialidase inhibitors could lead to a better understanding of these mechanisms. Also, given the wide prevalence and important role of sialidases in microbial infection, it is highly desirable to develop sialidase inhibitors to be used as anti-bacterial and anti-trypanosomal agents.
Though sialidases have long been identified in bacteria, the last twenty years have seen an explosion of bacterial sialidases purified and characterized due to the advance of molecular biological techniques. The explosion has also shed light on sialidase's role in bacterial metabolism, adherence, infection, and pathogenicity. Except for the active site, the bacterial sialidases do not exhibit an amino acid sequence similarity to the viral sialidases. Another characteristic of bacterial sialidases is the presence of non-sialidase related domains in the protein. These domains have other activities or functions which are beneficial to the bacteria. Many bacterial sialidases are membrane anchored, like the viral sialidases, while others are excreted extracellularly by the bacterium. Bacterial sialidases fall into two further subgroups based upon divalent metal requirements. The sialidase subgroup that requires a metal ion is represented by the Vibrio cholerae sialidase. The subgroup that does not require a metal ion for activity is represented by several bacterial sialidases, such as Clostridium perfringens, Clostridium sordelli, Microinotiospora viridifacieins, and Salmonella typhimurium among others. In addition to the high degree of sequence homology within the subgroup, the non-metal requiring sialidases also show a large amount of similarity to the N-terminal trans-sialidase domain of the trypanosomal trans-sialidase enzyme. The crystal structure for Salmonella typhimurium sialidase has been solved [Crennell, S. J., Garman, E. F., Laver, W. G., Vimr, E. R. & Taylor, G. L. (1993), The crystal structure of a bacterial sialidase (from Salmonella typhimurium LT2) shows the same fold as an influenza virus neuraminidase. Proc Nal Acad of Sci USA., 90, pp. 9852-6].